UNITED NATIONS (Reuters) - U.N. Secretary-General Ban Ki-moon expressed "grave concern" on Thursday over reports that Israeli jets bombed an apparent convoy of weapons near the Lebanese border and urged respect for the sovereignty of countries in the region.

Diplomats, Syrian rebels and regional security sources said on Wednesday that Israeli jets bombed a convoy near the Lebanese border, apparently hitting weapons destined for militant group Hezbollah. Syria denied the reports, saying the target of the air strikes had been a military research center northwest of Damascus.

"The Secretary-General notes with grave concern reports of Israeli air strikes in Syria," Ban's press office said in a statement. "At this time, the United Nations does not have details of the reported incident. Nor is the United Nations in a position to independently verify what has occurred."

"The Secretary-General calls on all concerned to prevent tensions or their escalation in the region, and to strictly abide by international law, in particular in respect of ... sovereignty of all countries in the region," the statement said.

U.N. peacekeepers in a demilitarized zone between Syria and Israel were also unable to verify a Syrian complaint that Israeli planes had flown over the Golan Heights to carry out the air strike.

Ban's spokesman, Eduardo del Buey, said Syrian authorities had protested to the U.N. peacekeeping mission, known as UNDOF, over the incident. The Syrian authorities said it was a violation of a disengagement accord that followed the last major war between the two countries, according to Syrian state media.

"UNDOF did not observe any planes flying over the area of separation and therefore was not able to confirm the incident. UNDOF also reported bad weather conditions," Del Buey said.

Lebanon regularly accuses Israel of violating its airspace.

The United Nations says more than 60,000 people have been killed during a 22-month-old revolt against Syrian President Bashar al-Assad, which began with peaceful protests but turned violent after Assad's forces tried to crush the demonstrations.

Israel captured the Golan Heights from Syria in a 1967 war. Syrian troops are not allowed in the area of separation under a 1973 ceasefire formalized in 1974. Israel and Syria are still technically at war.

Syria's civil war has spilled over into the zone, which had been largely quiet since the ceasefire. Stray shells and bullets have landed on the Israeli-controlled side and Israeli troops have fired shells into Syria in response.

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